Author: Sune Fischer
Date: 02:52:25 06/21/02
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On June 21, 2002 at 05:47:47, Koundinya Veluri wrote: >On June 21, 2002 at 05:12:28, Sune Fischer wrote: > >>On June 21, 2002 at 04:01:41, Sven Reichard wrote: >> >>>Maybe I'm missing something here, but if you furthermore agree to use a hash >>>table of size 2^i, i <= 32, you can replace all mods, divs and muls by a 32 bit >>>'and'. The performance hit of the slightly smaller table (less than factor 2) >>>should be outweighed by the faster access. >>> >>>just my 2 bits >> >>How do you know that? >>If you use power 2 size then you get pretty big jumps; 64,128,256,512. >>So you really have only 4 sizes of the hash. I think it is better to use 200 MB >>with modulo than 128 MB with AND (there are not divs or muls), the save is not >>_that_ much compared to what you save when getting those extra hashhits. >>Of course I don't _know_, I'm just guessing :) >> >>Some claim the distribution of the keys are better if the number of entries is >>prime, though I'm not convinced of that I can't rule it out. >> >>just my two øre. >>-S. >> >>>Sven. > >If you use two hash tables that use power 2 size, then there will be many more >total hash sizes to choose from. If you have 200 MB available, you can divide >that into 128 MB for one and 64 MB for the other, that's 192 MB total. > >Koundinya Then you would also need to do two memory lookups, so there goes your saving :) -S.
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